Extensive investigation and research work has been devoted to the development of traffic monitoring systems which mostly employ fixed pickup stations for integrating, processing, and broadcasting information to road users.
The detection and transmission arrangements are mostly based on either radar, inductive cable, radio, or steered wave transmission systems. Such monitoring systems have essentially the following limitations: updating is performed at long time intervals; local measurements are taken at far apart locations; and integrated and averaged information is generated which relates to the dynamic conditions of groups of vehicles, not to the individual vehicles.
Vehicle-to-vehicle interactive systems, based on the use of radar devices or transponders to provide drivers with indications of headway or distance (and its variations)between vehicles, have long been proposed but have been unsuccessful because either impractical or limited by their purely local character, covering vehicle pairs only.